A Rare Septuagenarian Patient with a Mild Form of Mucopolysaccharidosis Type IIIC with Ocular Manifestations: A Case Report.

INTRODUCTION: We present an atypical case of mucopolysaccharidosis (MPS) type IIIC to contribute to the growing understanding of its clinical heterogeneity and expand the known phenotypic spectrum of the disorder. This report describes one of the oldest known patients with genetically confirmed MPS IIIC. CASE PRESENTATION: The patient received genetic testing in her seventies, revealing variations in the HGSNAT and NAGLU genes, two genes associated with MPS III. Her clinical presentation consisted primarily of retinal dystrophy, diagnosed via clinical presentation in addition to OCT and ERG. The patient also showed signs of peripheral neuropathy which were initially presumed to be idiopathic. She did not exhibit the typical behavioral involvement and craniofacial abnormalities expected of MPS type IIIC. CONCLUSION: This presentation broadens the recognized clinical spectrum of MPS IIIC and may facilitate earlier diagnosis in adults with similar, seemingly idiopathic findings. Improved recognition of such atypical cases may support timely genetic testing and potential therapeutic options.